To check out the numeric options for kill, run the command:
% kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGEMT 8) SIGFPE 9) SIGKILL 10) SIGBUS 11) SIGSEGV 12) SIGSYS 13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGURG 17) SIGSTOP 18) SIGTSTP 19) SIGCONT 20) SIGCHLD 21) SIGTTIN 22) SIGTTOU 23) SIGIO 24) SIGXCPU 25) SIGXFSZ 26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGINFO 30) SIGUSR1 31) SIGUSR2
See man signal.
Signal 6 is SIGABRT -- see /usr/include/sys/signal.h. A process dying with this signal is usually due to it calling the abort(3) function. That generally indicates that the process itself has found that some essential pre-requisite for correct function is not available and voluntarily killing itself, rather than the process being killed by the kernel because it ran over resource limits or looked at memory addresses funny or something.